In
Celtic mythology,
Mag Mell ("plain of joy"), also called
Tir na n-Og ("land of youth"), was the
underworld. Unlike the underworld in most mythologies, Mag Mell was a pleasurable paradise, either an island or at the bottom of the ocean.
It was ruled by King Tethra, a Fomorian or Manannan mac Lir. Queen Niamh ruled Tir na n-Og.
See also: Aericura, Aillen